AWS Database Migration Service
User Guide (Version API Version 2016-01-01)

Replication Instances for AWS Database Migration Service

AWS DMS creates a replication instance that runs on an Amazon Elastic Compute Cloud (Amazon EC2) instance in a VPC based on the Amazon Virtual Private Cloud (Amazon VPC) service. You use this replication instance to perform the database migration. The replication instance provides high-availability and failover support using a Multi-AZ deployment when you select the Multi-AZ option. In a Multi-AZ deployment, AWS DMS automatically provisions and maintains a synchronous standby replica of the replication instance in a different Availability Zone. The primary replication instance is synchronously replicated across Availability Zones to a standby replica to provide data redundancy, eliminate I/O freezes, and minimize latency spikes.

                     AWS Database Migration Service replication instance

AWS DMS currently supports the T2 and C4 instance classes for replication instances. The T2 instance classes are low-cost standard instances designed to provide a baseline level of CPU performance with the ability to burst above the baseline. They are suitable for developing, configuring, and testing your database migration process, and for periodic data migration tasks that can benefit from the CPU burst capability. The C4 instance classes are designed to deliver the highest level of processor performance and achieve significantly higher packet per second (PPS) performance, lower network jitter, and lower network latency. You should use C4 instance classes if you are migrating large databases and want to minimize the migration time.

Each replication instance has a specific configuration of memory and vCPU. The following table shows the configuration for each replication instance type. For pricing information, see the AWS Database Migration Service pricing page.

Replication Instance Type


Memory (GB)

General Purpose













Compute Optimized













Public and Private Replication Instances

You can specify whether a replication instance has a public or private IP address that the instance uses to connect to the source and target databases. A replication instance should have a public IP address if the source or target database is located in a network that is not connected to the replication instance's VPC by using a virtual private network (VPN), AWS Direct Connect, or VPC peering.

A private replication instance has a private IP address that cannot be accessed outside the replication network. A replication instance should have a private IP address when both the source and target databases are located in the same network that is connected to the replication instance's VPC by using a VPN, AWS Direct Connect, or VPC peering.

A VPC peering connection is a networking connection between two VPCs that enables routing using each VPC’s private IP addresses as if they were in the same network. For more information about VPC peering, see VPC Peering in the Amazon VPC User Guide.

AWS DMS Maintenance Window

Periodically, AWS DMS performs maintenance on AWS DMS resources. Maintenance most often involves updates to the replication instance or the replication instance's operating system (OS). You can manage the time period for your maintenance window and see maintenance updates using the AWS CLI or AWS DMS API. The AWS DMS console is not currently supported for this work.

You can manually apply maintenance items at your convenience, or wait for the automatic maintenance process initiated by AWS DMS during your weekly maintenance window. You can find out whether a maintenance update is available for your replication instance by using the AWS CLI or AWS DMS API.

Maintenance items require that AWS DMS take your replication instance offline for a short time. Maintenance that requires a resource to be offline includes required operating system or instance patching. Required patching is automatically scheduled only for patches that are related to security and instance reliability. Such patching occurs infrequently (typically once or twice a year) and seldom requires more than a fraction of your maintenance window.

Use the DescribeReplicationInstances API action to determine if there are pending modifications to your replication instance and to see the current time period for your maintenance window. The PendingModifiedValues parameter indicates what parameter changes are pending. The PreferredMaintenanceWindow parameter shows the current time period for your maintenance window.

To change the time of the maintenance window, use the ModifyReplicationInstance API action and set the PreferredMaintenanceWindow parameter to your preferred time period.

The default maintenance window time period is determined by the AWS Region. The following table lists the maintenance window for each AWS Region that supports AWS DMS.

Region Time Block
Asia Pacific (Sydney) Region 12:00–20:00 UTC
Asia Pacific (Tokyo) Region 13:00–21:00 UTC
Asia Pacific (Mumbai) Region 17:30–01:30 UTC
Asia Pacific (Seoul) Region 13:00–21:00 UTC
Asia Pacific (Singapore) Region 14:00–22:00 UTC
Canada (Central) Region 06:29–14:29 UTC
EU (Frankfurt) Region 20:00–04:00 UTC
EU (Ireland) Region 22:00–06:00 UTC
EU (London) Region 06:00–14:00 UTC
South America (São Paulo) Region 23:00–07:00 UTC
US East (N. Virginia) Region 03:00–11:00 UTC
US East (Ohio) Region 03:00–11:00 UTC
US West (N. California) Region 06:00–14:00 UTC
US West (Oregon) Region 06:00–14:00 UTC

Replication Engine Versions

The replication engine is the core AWS DMS software that runs on your replication instance and performs the migration tasks you specify. AWS periodically releases new versions of the AWS DMS replication engine software, with new features and performance improvements. Each version of the replication engine software has its own version number, to distinguish it from other versions.

When you launch a new replication instance, it will run the latest AWS DMS engine version unless you specify otherwise. For more information, see Step 2: Create a Replication Instance in Getting Started.

If you have a replication instance that is currently running, you can upgrade it to a more recent engine version. (AWS DMS does not support engine version downgrades.) For more information, including a list of replication engine versions see Upgrading the Engine Version of a Replication Instance .